This invention relates generally to a relief valve system for controlling the pressure on both the discharge and inlet side of a pump.
The relief valve system of the invention provides the complete pressure protection that is not available with the conventional systems which generally comprise a recirculating relief valve or an engine governor. Occasionally, a separate dump relief valve is additionally installed on the inlet side for pump inlet pressure relief. The conventional recirculating relief valves simply dump excess water back to the inlet side of the pump to relieve pressure. This arrangement is satisfactory under conditions where the intake pressure is considerably less than the discharge pressure. However, in actual practice, such as in firefighting applications, this may not be the case. For example, there may be a strong (high pressure) hydrant water supply to the pump, or the pump may be included in a pump relay hook-up. It is especially important to relieve excessive pressure conditions on pumps used in firefighting because an excessive pressure could create an unsafe condition for the hose operator.
While an engine governor throttles back the engine to reduce the discharge pressure, this also may not completely compensate for the high incoming pressure so that additional pressure relief means are necessary.
Also, while a suction dump valve will partially counteract the above-described problems of conventional systems, such a dump valve is limited because it is usually preset and cannot be easily adjusted to compensate for all the pumping conditions under which the pump must be used.
The relief valve system in accordance with the invention comprises control means which are responsive to the occurrence of an excessive pressure on the inlet or discharge side of the pump to relieve this condition by dumping excess pressure to atmosphere. In one system a novel control means is arranged to control a relief valve on the inlet side of the pump so as to dump the inlet flow to atmosphere. In another system a relief valve is controlled to dump the discharge flow to atmosphere. It is noted that locating the relief valve on the discharge side of the pump eliminates problems that frequently occur with suction side dump valves, such as clogging with debris and sticking open so as to subsequently interfere with priming of the pump.